Fuel Flow Testing

[Av8r_Sed]

Is it possible to temporarily bypass the fuel flow transducer and repeat your level flight test? Also, you have to cast a suspicious eye at any valves in the system. These are often restriction points.

[jiott]

I only have one main fuel shutoff valve in the system.

Jim

[jtpitkin06]

My kit was supplied with a brass step down adapter coming out of the tank. Then fuel had to flow through a ninety degree brass elbow with a hose barb. Brass 90 degree fittings are notorious for restricting fuel flow.
It is better to use a larger elbow to change direction at the tank, then step down with a straight barb fitting to attach your hose. I suspect that is where your flow resistance is located.

The best set up would be to use AN or Airquip full flow ips-to-hose fittings.

John

[SkyPirate]

don't forget your fuel caps get pressure in flight , if you could somehow charge your tank to equal the static pressure in flight,..an old ASI to gauge the pressure at cruise?it cant be much pressure but it might increase the flow a bit

[DesertFox4]

Jim- you should see a better flow rate than that. You might try it at the firewall fitting and see if it is still slow there . You can always start working your way back to the fuel tanks checking flow as you go. I know it's a pain but this system has to flow correctly for safe flight.
Your air return line must be routed properly and not pinched anywhere as it goes from header tank back up to the right wing tank.
I'll assume you sloshed your fuel tanks as prescribed and checked your fuel strainers for blockages. Check your fuel caps to make sure they are letting air in as fuel flows out. Blow through the ram air tubes and make sure they are open and functioning. Just a couple things I could think of quickly.
Photos of your system may help with suggestions. Good luck.

P.S. fuel filters should be considered also. Did you check them for contamination or blockage?

[jiott]

I was hoping to get some actual test flow rates that you guys got when doing this test. All my fittings and routings are kit supplied and per the book. Is it common to have to upsize the kit fittings as John suggested? The manual doesn't even say to do this test. I have a suspision that many builders just build by the book, then go fly.

Jim

[Dorsal]

I know I built mine according to the manual, checked that I had decent flow but did not measure it and flew it. I may measure the flow and let you know.